1. Field of the Invention
This invention relates generally to underground mine personnel doors and, more specifically, to underground mine personnel doors formed from substantially noncombustible materials and that are constructed to withstand heat generated during an underground mine fire.
2. State of the Art
In underground mining, ventilation is a primary concern to ensure air quality for those personnel working underground. Accordingly, walls (commonly referred to as "stoppings"), typically constructed of masonry materials, are required to be erected every 300 feet in seam heights below 48 inches and every 600 feet in seam heights 48 inches or higher. The main purpose for such stoppings is to control ventilation within the mine, that is to block air flow through certain passages and to direct the flow of fresh air to other passages where miners are actively working. The stoppings secondarily act as fire barriers in case of an underground mine fire to contain the fire and smoke between stoppings. In order to allow passage of personnel and equipment, personnel doors are built into the stoppings.
Under 30 C.F.R. .sctn. 75.333, personnel doors are required to be "constructed of noncombustible material and shall be of sufficient strength to serve their intended purpose of maintaining separation and permitting travel between air courses." One method of testing such doors under fire-like conditions is provided in ASTM E119-88, Standard Test Methods for Fire Tests of Building Construction and Materials, which subjects the test specimen to increasing temperatures up to 1700.degree. F. in one hour under positive pressure. In order to sufficiently pass this test, a mine door must be able to maintain its seal between the door and the door frame during the entire duration of the test.
Despite these requirements, as described in U.S. Pat. No. Re. 34,053 to Kennedy et al., manufacturers of mine doors typically use seal members made of rubber or the like (column 6, lines 17-19). During a fire, however, such seals will burn, thus severely, if not totally, diminishing the integrity of the seal. In addition, the construction of the doors is typically not sufficient to prevent the door itself from failing structurally in the event of a fire. During a fire, the high temperatures may cause doors and frames to warp and hinges and latches to fail. Warping or any failure of hardware supporting or securing the door to the frame may cause the door panel to separate from the frame resulting in loss of integrity of the seal between the door and the frame. If such seal integrity is lost during a mine fire, the fire may be allowed to spread passed the stopping, or, at the least, allow smoke to flow between the door and the door frame. There have been attempts in the art to make such doors fire resistant. For example, in SU 860769 to Vasilenko et al., a mine door is provided with a perforated elastic sleeve that runs around the perimeter of the door and is connected to a water supply. In the event of a fire, a temperature sensor signals a valve to be opened, releasing water through the elastic sleeve to cool the door. Other liquid or gas delivery systems have also been employed with mine doors, but such systems are quite complex and expensive.
Thus, it would be advantageous to provide a mine door that is comprised of noncombustible materials as required by 30 C.F.R. .sctn. 75.333, that can withstand a fire test, such as the fire test provided in ASTM E119-88, and accordingly that has a high probability of substantially maintaining its seal in the event of a mine fire. It would also be advantageous to provide such a mine door that is relatively simple and inexpensive to fabricate.